(307d) Morphological Characterization and Pore-Scale Simulations of Gde Catalyst Layer and Microporous Layer for Electrochemical CO2 Reduction

Gas diffusion electrodes (GDEs) help reducing CO₂ transport resistances in devices for electrochemical CO₂ reduction. The influence of the mesoscale morphology of the catalyst layer (CL) and microporous layer (MPL) on the device performance is unknown, and quantifying it is challenging. Furthermore, different wetting regimes affect GDEs activity and selectivity. We use a combined experimental-numerical technique to characterize transport properties and operando conditions in different hydration regimes.

CL structures are characterized by FIB-SEM nano-tomography: after epoxy embedding, a focused ion beam mills the sample and a series of cross-sectional images are acquired with a scanning electron microscope. The images are processed and segmented to reconstruct the exact 3D morphology of the material with an isotropic resolution down to 4 nm. Addition of Cu(Ac)₂ in the resin allows to obtain contrast between the embedding epoxy and the C-based MPL in the backscattered electrons images, and therefore segment from the same image the MPL and the CL.

A series of morphological descriptors are extracted from a set of digitalized Cu and Ag based CLs. The structures are then considered as geometric domains in computational fluid dynamics (CFD) simulations to extract tensors of effective diffusion coefficient, permeability, tortuosity, and effective solid conductivity. The properties vary depending on the direction of diffusion and flow, and samples with similar synthesis protocols exhibit different transport properties. An Ag-based GDE is used for direct multiphase pore-scale simulations with the CL and the MPL in different wetting conditions. We show the existence of an optimal wetting regime and the corresponding local conditions.

Our combined experimental-numerical approach accurately characterizes the mesoscale morphology and transport properties of CLs and MPLs. Furthermore, the effect of wetting regimes on GDE activity was investigated. Overall, our results clarify pore-scale conditions and contribute to more efficient modeling of GDEs for CO₂ reduction.